Same-sex marriage has been a constant political and social theme in recent months, but not for the reasons it made news this weekend.

Item one: The daughters of former vice president Dick Cheney – Mary and Liz – went public with their differences over gay marriage, revealing the kind of debate no doubt happening in other American families.

In a ceremony at the Kennedy Center Saturday evening, Justice Ginsburg performed the wedding of Michael Kaiser, who runs the John F. Kennedy Center for the Performing Arts, and John Roberts.

No, not that John Roberts, the Chief Justice of the Supreme Court, but government economist John Roberts, who works at the Commodity Futures Trading Commission.

Mr. Kaiser is an old friend of Justice Ginsburg, described by the Washington Post as “perhaps the Supreme Court’s most ardent supporter of the fine arts, especially opera.”

Ginsburg, the senior liberal on the court, has been on the pro-gay-marriage side of recent 5-4 Supreme Court decisions invalidating the federal Defense of Marriage Act (DOMA) and opening the way for California to resume same-sex marriages.

Saturday evening’s wedding at the Kennedy Center, Ginsburg told the Washington Post, “will be one more statement that people who love each other and want to live together should be able to enjoy the blessings and the strife in the marriage relationship.” She has agreed to officiate at another same-sex wedding later this month.

It’s not unusual for Supreme Court justices to perform marriage ceremonies. Ginsburg did for her son and his wife. Associate Justice Clarence Thomas did for radio broadcaster and fellow conservative Rush Limbaugh and his third wife.

Of the two, Liz has been the most politically outspoken, a strong advocate for conservative causes and frequently tearing into President Obama during her 18-month stint as a Fox News contributor.

She recently announced that she will challenge US Sen. Mike Enzi (R) of Wyoming in the Republican primary election next year.

Her father represented Wyoming in the US House of Representatives from 1979 to 1989, but she lived in Washington, DC from girlhood through a series of federal government jobs in the administration of George W. Bush. She moved to Wyoming last year, but claiming it as her home state has been a challenge.

As part of establishing her bona fides as a conservative in a red state, Ms. Cheney recently declared her opposition to same-sex marriage.

“I believe the issue of marriage must be decided by the states, and by the people in the states, not by judges and not even by legislators, but by the people themselves,” she said in a statement last week. “I am strongly pro-life and I am not pro-gay marriage.”

The problem for her family is that her younger sister Mary is married to her long-time partner Heather Poe (with whom she has two children), and the sisters’ father announced his support for same-sex marriage in 2009 – the year after he and Mr. Bush left office.

“At the National Press Club in Washington that year, Cheney said, "As many of you know, one of my daughters is gay and it is something we have lived with for a long time in our family."

"I think people ought to be free to enter into any kind of union they wish. Any kind of arrangement they wish,” he said, although he added that he – like Liz – believes that should be decided on a state-by-state basis.

Mary Cheney, who leads a quiet, nonpolitical life, could not let her older sister’s recent comments on gay marriage stand without responding. After all, just this year she had signed a Supreme Court friend-of-the-court brief supporting same-sex marriage.

"For the record, I love my sister, but she is dead wrong on the issue of marriage," Mary wrote on her Facebook page. "Freedom means freedom for everyone. That means that all families – regardless of how they look or how they are made – all families are entitled to the same rights, privileges and protections as every other."